A conventional plastic semiconductor package includes a semiconductor die wire bonded to a lead frame, and encapsulated in a plastic body. One consideration in designing a plastic package is heat transfer from the die. Operation of the integrated circuits within the die generate heat which must be dissipated. In a conventional plastic semiconductor package, the bulk of heat transfer from the encapsulated die is through the terminal leads of the package. However, as circuit densities increase, semiconductor dice generate additional heat, and the leads of the package are not always able to efficiently dissipate the heat.
This has led to the development of semiconductor packages that include a heat sink. Typically, the heat sink comprises a metal plate embedded in the plastic body of the package. Representative heat sink packages are described in U.S. Pat. No. 5,666,003 entitled "Packaged Semiconductor Device Incorporating Heat Sink Plate", and in U.S. Pat. No. 5,629,561 entitled "Semiconductor Package With Integral Heat Dissipator".
One consideration in packages that incorporate a heat sink is the thermal path from the die to heat sink. In some designs the thermal path may depend on direct contact of the die with the heat sink. However, the contact areas between the die and the heat sink may have a relatively small surface area. In other designs, the heat sink may not have direct contact with the die, but rather is in contact with the lead frame. The thermal path from the die to the heat sink is thus through the lead frame. This thermal path may not be as efficient as is desirable for dissipating as much heat as possible from the die.
Another consideration in packages that incorporate a heat sink is heat transfer from the heat sink to the environment. In most electronic assemblies that incorporate heat sink semiconductor packages, heat transfer to the environment is by convection to the air. Alternately, a liquid coolant can be used to transfer heat from the individual packages or from the assembly as a whole.
It would be advantageous for a heat sink to provide efficient heat transfer not only from the die, but also from the die to the environment. The present invention is directed to a semiconductor package that includes multiple heat sink elements having efficient heat transfer paths to the die, and to the environment. In addition, the semiconductor package is constructed such that the heat sinks on adjacent packages of an electronic assembly can be interlocked to maintain physical and thermal contact therebetween.